1. Technical Field
The present invention relates in general to a method and system for improved data communication and in particular to an improved method and system for efficient non-coherent demodulation of frequency shift keyed signals. Still more particularly, the present invention relates to an improved method and system for efficient non-coherent demodulation of frequency shift keyed signals by reducing the rate of computation required from a demodulation process on a digital signal processor.
2. Description of the Related Art
Data processing systems may transmit information, via a modem, to data processing systems at remote sites by utilizing a telephone line for transmitting frequency shift keyed ("FSK") signals. Generally in FSK, each data state is assigned a discrete frequency for transmission over a band limited channel, which prevents abrupt frequency changes between data intervals. Consequently, FSK signals show gradual changes or transitions between frequencies.
At a receiving end of a FSK transmission, the FSK signal must be demodulated in order to recreate the original signal. Non-coherent demodulation of FSK signals typically requires computation of the receiver algorithm at the sample rate which is typically eight or more times the baud rate. This frequent sampling is required because of the necessity of a post detection filter utilized to filter out frequency components at twice the carrier frequency which are generated during the demodulation process. To receive asynchronous characters utilizing a Start-Stop protocol, a universal asynchronous receiver/transmitter ("UART") typically requires an input from the demodulator which includes all of the samples in order to accurately find the center of each bit period for optimum sampling of the data stream. A bit period is the width of a pulse representing a bit of data.
Consequently, it would be desirable to have a method and system for reducing the number of computations required from a demodulator in demodulating FSK signals.